The present invention relates to an improved character recognition apparatus. The handling of mail, bank checks and the like is speeded up by a tremendous extent by optoelectronically reading and processing characters on the documents. In the case of mail sorting, a character recognition apparatus reads the zip codes on the envelopes and automatically routes the mail to the correct carrier.
Such character recognition apparatus generally functions to optoelectronically scan a character in a rectangular pattern of lines and produce quantized, binary electronic signals corresponding to the character pattern. The quantized character pattern is stored in a memory and compared on a bit to bit basis with character patterns of standard characters. The unknown character is defined to correspond to the standard character producing the closest correlation.
The major problem in character recognition occurs where it is required to recognize handwritten characters. Since each person has a different way of writing a particular letter or number, the correlation between a handwritten character and the corresponding standard character varies to the extent that characters are often erroneously recognized as different characters. For example, where the number "8" is written in such a manner that the lower portion thereof is significantly smaller than the upper portion thereof, it is often incorrectly recognized as the number "9."
Various preprocessing operations are usually performed prior to the recognition step to normalize the size, position and slant of the character and thereby increase the correlation. However, prior art character recognition devices still produce frequent errors in recognizing handwritten characters and require a very large memory for storing the character patterns. In order to enable horizontal normalization of a character pattern, a memory having a horizontal size equal to twice the actual horizontal character size is often provided, adding unnecessarily to the size and cost of the apparatus.
A function widely used in character recognition is known in the art as a quadratic identification or correlation function. While such a function produces accurate recognition of normal characters, the correlation is far from satisfactory where the characters are distorted from their normal shape.